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- Title
Cyclic AMP-mediated inhibition of gallbladder contractility: role of K+ channel activation and Ca2+ signaling.
- Authors
Morales, Sara; Camello, Pedro J.; Mawe, Gary M.; Pozo, Imaria J.; Pozo, María J
- Abstract
We have examined the mechanisms of cAMP-induced gallbladder relaxation by recording isometric tension and membrane potential in the intact tissue, and global intracellular calcium concentrations ([Ca(2+)](i)) and F-actin content in isolated myocytes. Both the phosphodiesterase (PDE) inhibitor, IBMX (100 microM) and the adenylate cyclase activator, forskolin (2 microM) caused decreases in basal tone that exhibited similar kinetics. IBMX and forskolin both caused concentration dependent, right-downward shifts in the concentration-response curves of KCl and cholecystokinin (CCK). IBMX and forskolin elicited a membrane hyperpolarization that was almost completely inhibited by the ATP-sensitive K(+) channel (K(ATP)) channel blocker, glibenclamide (10 microM). IBMX also induced an increase in large-conductance Ca(2+)-dependent K(+) (BK) channel currents, although the simultaneous blockade of BK and K(ATP) channels did not block IBMX- and forskolin-induced relaxations. Ca(2+) influx activated by L-type Ca(2+) channel activation or store depletion was also impaired by IBMX and forskolin, indicating a general impairment in Ca(2+) entry mechanisms. IBMX also decreases [Ca(2+)](i) transients activated by CCK and 3,6-Di-O-Bt-IP(4)-PM, a membrane permeable analog of inositol triphosphate, indicating an impairment in Ca(2+) release through IP(3) receptors. Ionomycin-induced [Ca(2+)](i) transients were not altered by IBMX, but the contractile effects of the Ca(2+) ionophore were reduced in the presence of IBMX, suggesting that cAMP can decrease Ca(2+) sensitivity of the contractile apparatus. A depolymerization of the thin filament could be reason for this change, as forskolin induced a decrease in F-actin content. In conclusion, these findings suggest that multiple, redundant intracellular processes are affected by cAMP to induce gallbladder relaxation.
- Subjects
GALLBLADDER; BIOLOGICAL membranes; CALCIUM; MUSCLE cells; ADENYLATE cyclase; ADENOSINE triphosphate; POTASSIUM metabolism; SMOOTH muscle physiology; ANIMAL experimentation; CELLULAR signal transduction; COMPARATIVE studies; CYCLIC adenylic acid; DIGESTION; DOSE-effect relationship in pharmacology; GUINEA pigs; RESEARCH methodology; MEDICAL cooperation; MUSCLE contraction; POTASSIUM; RESEARCH; RESEARCH funding; SMOOTH muscle; THEOPHYLLINE; EVALUATION research; IN vitro studies; CHEMICAL inhibitors; PHARMACODYNAMICS
- Publication
British Journal of Pharmacology, 2004, Vol 143, Issue 8, p994
- ISSN
0007-1188
- Publication type
journal article
- DOI
10.1038/sj.bjp.0706006