Effect of vasopressin on intracellular [Ca] and Na transport in cultured toad bladder cells.
Intracellular free [Ca] [( Ca]i) and transepithelial sodium transport were measured simultaneously in cultured toad bladder cells grown on collagen-coated filters. [Ca]i was measured with fura-2 and fluorescence microscopy while sodium transport was measured as the short-circuit current (Isc) with a voltage clamp. Following stimulation with vasopressin [Ca]i and Isc rose in parallel to maximal values within 10 min. [Ca]i increased from 65 +/- 5 to 123 +/- 12 nM and Isc, from 11 +/- 3 to 25 +/- 6 microA (n = 4). The vasopressin-induced rise in [Ca]i correlated significantly with the increase in Isc, suggesting that the rise in [Ca]i might be necessary for the increase in Isc. If so, then adenosine 3',5'-cyclic monophosphate (cAMP), which mimics the natriferic action of vasopressin, should also increase [Ca]i. Although cAMP increased [Ca]i to a peak value of 32 +/- 13% (P less than 0.05) above control at 10 min, the rise in Isc did not parallel the increase in [Ca]i. Isc peaked instead at 20 min, rising to 114 +/- 25% (P less than 0.05) over control, during which time [Ca]i returned to base line. This result suggested that a steady state increase in [Ca]i was not necessary for the natriferic action of cAMP. This notion was confirmed in experiments in which the vasopressin-induced increase in [Ca]i was prevented by bathing the tissue in a low-[Ca] buffer. Under these conditions, Isc increased 37 +/- 9% above control (P less than 0.05, n = 4) even though [Ca]i remained largely unchanged. Our results suggest that although vasopressin increases [Ca]i in toad bladder cells, the rise in [Ca]i does not seem to play a role in the natriferic response. These experiments also demonstrate the utility of making simultaneous measurements of ion transport and [Ca]i, which allow direct examination of calcium's role in mediating ion transport.
Wong
S M
SM
Department of Medicine, Columbia College of Physicians and Surgeons, New York, New York 10032.
Chase
H S
HS
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001572:Benzofurans; D001692:Biological Transport / Q000187:drug effects; D002025:Bufonidae; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000494:pharmacology; D004553:Electric Conductivity; D004848:Epithelium / Q000378:metabolism; D005456:Fluorescent Dyes; D016257:Fura-2; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D008856:Microscopy, Fluorescence; D012964:Sodium / Q000378:metabolism*; D001743:Urinary Bladder / Q000187:drug effects / Q000378:metabolism*; D014667:Vasopressins / Q000494:pharmacology*
D001572:Benzofurans; D002121:Calcium Channel Blockers; D005456:Fluorescent Dyes; D014667:Vasopressins; C006014:8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate; D005707:Gallic Acid; D000584:Amiloride; D012964:Sodium; D000242:Cyclic AMP; D002118:Calcium; D016257:Fura-2