Mobilization of intracellular Ca2+ by thromboxane A(2) does not affect Ca2+-activated K+ channels in rat colonic crypt cells

The effects of 9,11-epithio-11,12-methano-thromboxane A(2) (STA(2)), a stab le thromboxane A(2) analogue, and carbachol on colonic Ca2+-activated K+ ch annels were studied. in indo-1-loaded single cells in isolated rat colonic crypts, both STA(2) (0.1 mu M) and carbachol (10 mu M) transiently increase d intracellular free Ca2+ concentration ([Ca2+](i)) by 136 and 155 nM, resp ectively. In whole-cell current-clamp experiments of the colonic crypt cell s with Cl--free solutions, carbachol (10 mu M) hyperpolarized the cell by 1 9.7 mV, while STA(2) (0.1 mu M) did not affect the membrane potential. In t he isolated colonic mucosa that was permeabilized mucosally by a monovalent ionophore nystatin in the presence of a serosally directed K+ gradient, ca rbachol (10 mu M) transiently elicited K+ current, but STA(2) (0.1 mu M) di d not. These results indicate that STA(2) elevates [Ca2+](i) in rat colonic crypt cells but does not activate basolateral Ca2+-activated K+ channels.