title: Membrane potential and conductance of frog skin gland acinar cells in resting conditions and during stimulation with agonists of macroscopic secretion.
abstract: Frog skin glands were stripped of connective tissue and investigated using the nystatin-permeabilized whole-cell patch-clamp configuration. The membrane potential in unstimulated acinar cells was -69.5+/-0.7 mV, and the conductance was dominated by K+, based on ion substitution experiments. The cells were electrically coupled through heptanol- and halothane-sensitive gap junctions. During application of gap junction blockers, the whole-cell current/voltage relationship displayed strong outward rectification. Outward currents were blocked by barium. Stimulation by agonists known to cause increases in either cytosolic cAMP ([cAMP]c) (isoproterenol, prostaglandin E2, both at 2 microM) or free cellular Ca2+ concentration ([Ca2+]c) (noradrenaline, 10 microM, added with propranolol, 5 microM; carbachol, 100 microM) in the frog skin glands caused reversible depolarization: by 34+/-3 mV, 36+/-3 mV, 25+/-3 mV (plateau-phase), and 20+/-3 mV, respectively. Ion substitution experiments showed that stimulation through either pathway (cAMP or Ca2+) resulted in the activation of a Cl- conductance. Application of noradrenaline or adrenaline resulted in a faster depolarization (rates 22 mV/s, 26 mV/s) than stimulation by isoproterenol or prostaglandin E2 (5.6-5.7 mV/s). Cells that were depolarized by exposure to isoproterenol or prostaglandin E2 partially repolarized when stimulated by noradrenaline. The repolarization was blocked by Ba2+ (5 mM) or prazosine (1 microM), consistent with the activation of Ca(2+)-dependent K+ channels via alpha1-adrenergic receptors. We conclude that in the frog skin gland both Ca(2+)-dependent and cAMP-dependent Cl- channels are present in the apical membrane. Increases in free [Ca2+]c in the cAMP-stimulated gland results in the activation of K+ channels, thereby increasing the driving force for Cl- exit.
authors.affiliation: Department of Zoophysiology, August Krogh Institute, University of Copenhagen, Denmark. JBSorensen@aki.ku.dk
authors.forename: J B
authors.initials: JB
authors.lastname: Sørensen
authors.forename: E H
authors.initials: EH
authors.lastname: Larsen
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D002217:Carbachol / Q000494:pharmacology; D018118:Chloride Channels / Q000187:drug effects / Q000502:physiology; D000242:Cyclic AMP / Q000502:physiology; D004558:Electric Stimulation; D004594:Electrophysiology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D005088:Exocrine Glands / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D005260:Female; D017629:Gap Junctions / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018721:Muscarinic Agonists / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D011893:Rana esculenta; D012867:Skin / Q000187:drug effects* / Q000378:metabolism; D013268:Stimulation, Chemical
chemical_list: D000316:Adrenergic alpha-Agonists; D015220:Calcium Channels; D018118:Chloride Channels; D018721:Muscarinic Agonists; D015221:Potassium Channels; D002217:Carbachol; D000242:Cyclic AMP; D009638:Norepinephrine