Quantification of Ca2+-activated K+ channels under hormonal control in pig pancreas acinar cells.
Ca2+- and voltage-activated K+ channels are found in many electrically excitable cells and have an important role in regulating electrical activity. Recently, the large K+ channel has been found in the baso-lateral plasma membranes of salivary gland acinar cells, where it may be important in the regulation of salt transport. Using patch-clamp methods to record single-channel currents from excised fragments of baso-lateral acinar cell membranes in combination with current recordings from isolated single acinar cells and two- and three-cell clusters, we have now for the first time characterized the K+ channels quantitatively. In pig pancreatic acini there are 25-60 K+ channels per cell with a maximal single channel conductance of about 200 pS. We have quantified the relationship between internal ionized Ca2+ concentration [( Ca2+]i) membrane potential and open-state probability (p) of the K+ channel. By comparing curves obtained from excised patches relating membrane potential to p, at different levels of [Ca2+]i, with similar curves obtained from intact cells, [Ca2+]i in resting acinar cells was found to be between 10(-8) and 10(-7) M. In microelectrode experiments acetylcholine (ACh), gastrin-cholecystokinin (CCK) as well as bombesin peptides evoked Ca2+-dependent opening of the K+ conductance pathway, resulting in membrane hyperpolarization. The large K+ channel, which is under strict dual control by internal Ca2+ and voltage, may provide a crucial link between hormone-evoked increase in internal Ca2+ concentration and the resulting NaCl-rich fluid secretion.
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001839:Bombesin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002766:Cholecystokinin / Q000494:pharmacology; D066298:In Vitro Techniques; D007473:Ion Channels / Q000502:physiology*; D008564:Membrane Potentials; D010179:Pancreas / Q000502:physiology*; D011188:Potassium / Q000502:physiology*; D013552:Swine
D007473:Ion Channels; D002766:Cholecystokinin; D000109:Acetylcholine; D001839:Bombesin; D011188:Potassium; D002118:Calcium