Somatotropes and GC cells, a GH-producing cell line, exhibit [Ca2+]i oscillations that result from rhythmic Ca2+ action potentials. Determination of this operating mode required simultaneous recording of both parameters by fura-2 imaging and patch-clamp techniques. In order to test whether patch recording induces artificial alteration of the [Ca2+]i oscillatory pattern, we recorded separately or simultaneously [Ca2+]i and membrane potential. In the absence of any other stimulation, seal formation in patch-clamp recording evoked by itself a 2.5- to 4-fold persistent increase in basal [Ca2+]i, speeded up their frequency (from 0.03–0.17 to 0.4 Hz) and changed their pattern to a tonic mode. Patch-induced [Ca2+]i increase was reproduced by mechanical contact between the pipette and the membrane. It was reduced by nifedipine, a blocker of L-type Ca2+ channels, as well as by removal of external Na+. It was fully blocked by external Ca2+ removal or gadolinium. All patch-clamp-induced perturbations were reversed by membrane hyperpolarization. We propose that patch-clamp recording evokes Ca2+ entry through L-type Ca2+ channels either directly, or indirectly via membrane depolarization. This shows that patch recordings in endocrine cells showing mechanosensitivity have to be interpreted with caution, and explains why long-lasting patch recordings are so difficult to obtain.

Kwiecien R, Hammond C: Differential management of Ca2+ oscillations by anterior pituitary cells: A comparative overview. Neuroendocrinology 1998;68:135–151.
Tashjian AH Jr, Yasumura Y, Levine L, Sato GH, Parker ML: Establishment of clonal strains of rat pituitary tumor cells that secrete growth hormone. Endocrinology 1968;82:342–352.
Kwiecien R, Tseeb V, Kurchikov A, Kordon C, Hammond C: Growth hormone-releasing hormone triggers pacemaker activity and persistent Ca2+ oscillations in rat somatotrophs. J Physiol (Lond) 1997;499:613–623.
Kwiecien R, Robert C, Cannon R, Vigues S, Arnoux A, Kordon C, Hammond C: Endogenous pacemaker activity of rat tumour somatotrophs. J Physiol (Lond) 1998;508:883–905.
Grynkiewicz G, Poenie M, Tsien RY: A new generation of calcium indicators with greatly improved fluorescence properties. J Biol Chem 1985;260:3440–3450.
Bresson-Bépoldin L, Dufy-Barbe L: GHRP-6 induces a biphasic calcium response in rat pituitary somatotrophs. Cell Calcium 1994;15:247–258.
Cuttler L, Glaum SR, Collins BA: Calcium signalling in single growth hormone-releasing factor-responsive pituitary cells. Endocrinology 1992;130:945–953.
Holl RW, Thorner MO, Leong DA: Intracellular calcium concentration and growth hormone secretion in individual somatotropes: Effects of growth hormone-releasing factor and somatostatin. Endocrinology 1988;122:2927–2932.
Docherty RJ: Gadolinium selectively blocks a component of calcium current in rodent neuroblastoma × glioma hybrid (NG108-15) cells. J Physiol (Lond) 1988;398:33–47.
Yang XC, Sachs F: Block of stretch-activated ion channels in Xenopus oocytes by gadolinium and calcium ions. Science 1989;243:1068–1071.
Ben-Tabou S, Keller E, Nussinovitch I: Mechanosensitivity of voltage-gated calcium currents in rat anterior pituitary cells. J Physiol (Lond) 1994;476:29–39.
Chen Y, Simasko SM, Niggel J, Sigurdson WJ, Sachs F: Calcium uptake in GH3 cells during hypotonic swelling: The sensory role of stretch-activated ion channels. Am J Physiol 1996;270:C1790–1798.
Kato M, Sakuma Y: Regulation by growth hormone-releasing hormone and somatostatin of a Na+ current in the primary cultured rat somatotroph. Endocrinology 1997;138:5096–5100.
Takano K, Takei T, Teramoto A, Yamashita N: GHRH activates a non-selective cation current in human GH-secreting adenoma cells. Am J Physiol 1996;270:E1050–E1057.
Simasko SM: A background sodium conductance is necessary for spontaneous depolarizations in rat pituitary cell line GH3. Am J Physiol 1994;266:C709–C719.
Kato M, Hoyland J, Sikdar SK, Mason WT: Imaging of intracellular calcium in rat anterior pituitary cells in response to growth hormone releasing factor. J Physiol (Lond) 1992;447:171–189.
Kato M, Hattori MA, Suzuki M: Inhibition by extracellular Na+ replacement of GRF-induced GH secretion from rat pituitary cells. Am J Physiol 1988;254:E476–E481.
Kato M, Suzuki M: Effect of Li+ substitution for extracellular Na+ on GRF-induced GH secretion from rat pituitary cells. Am J Physiol 1989;256:C712–718.
Ando J, Ohtsuda A, Katayama Y, Korenaga R, Ishikawa C, Kamiya A: Intracellular calcium response to directly applied mechanical shearing force in cultured vascular endothelial cells. Biorheology 1994;31:57–68.
Bülow A, Johansson B: Membrane stretch evoked cell swelling increases contractile activity in smooth muscle through dihydropyridine-sensitive pathways. Acta Physiol Scand 1994;152:419–427.
Setoguchi M, Ohya Y, Abe I, Fujishima M: Stretch-activated whole-cell currents in smooth muscle from mesenteric resistance artery of guinea pig. J Physiol (Lond) 1997;501:343–353.
Sigurdson W, Ruknudin A, Sachs F: Calcium-imaging of mechanically-induced fluxes in tissue-cultured chick heart: Role of stretch-activated ion channels. Am J Physiol 1992;262:H1110–1115.
Tatsukawa Y, Kiyosue T, Arita M: Mechanical stretch increases intracellular calcium concentration in cultured ventricular cells from neonatal rats. Heart Vessels 1997;12:128–135.
Stalmans P, Himpens B: Confocal imaging of calcium signaling in cultured rat retinal pigment epithelial cells during mechanical and pharmacological stimulation. Invest Ophthalmol Vis Sci 1997;38:176–187.
Churchill GC, Atkinson MM, Louis CF: Mechanical stimulation initiates cell to cell calcium signaling in ovine lens epithelial cells. J Cell Sci 1996;109:355–365.
Hu H, Sachs F: Mechanically-activated currents in chick heart cells. J Membr Biol 1996;154:205–216.
Marchenko SM, Sage SO: A novel mechanosensitive cationic channel from the endothelium of rat aorta. J Physiol (Lond) 1997;498:419–425.
Sachs F, Morris CE: Mechanosensitive ion channels in nonspecialized cells. Rev Physiol Biochem Pharmacol 1998;132:1–77.
Watanabe SI, Tanizaki M, Kaneko A: Two types of stretch-activated channels coexist in the rabbit corneal epithelial cell. Exp Eye Res 1997;64:1027–1035.
Copyright / Drug Dosage / Disclaimer
Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.
You do not currently have access to this content.