Smooth muscle from gallbladders with
cholesterol stones exhibits impaired response to
cholecystokinin (CCK). This study investigated whether the impaired response is mediated by different signal-transduction pathways responsible for CCK-induced contraction in prairie dog and human gallbladders with
cholesterol stones. Gallbladder muscle cells were isolated enzymatically to study contraction.
Protein kinase C (PKC) activity was measured by examining the phosphorylation of a specific substrate
peptide from
myelin basic protein Ac-MBP-(4-14). Gallbladder muscle cells from high-
cholesterol-fed prairie dogs contracted less in response to CCK octapeptide (CCK-8) than those from the control group. However, inositol-1,4,5-trisphosphate (IP3),
diacylglycerol, and
guanosine 5'-O-(3-thiotriphosphate) induced the same magnitudes of contraction in these two groups. In control prairie dog and human gallbladders, the maximal contraction caused by 10(-8) M
CCK-8 was blocked by the
calmodulin antagonist CGS9343B but not by the PKC inhibitor
H-7. Conversely, in gallbladders with
cholesterol stones from prairie dogs or human patients, the maximal contraction induced by 10(-8) M
CCK-8 was blocked by
H-7 and
chelerythrine but not by CGS9343B. In these gallbladders
CCK-8 caused a significant PKC translocation from the cytosol to the membrane. High CCK concentrations may activate the
calmodulin-dependent pathway in functionally normal gallbladder muscle and the PKC-dependent pathway in muscle from gallbladders with
cholesterol stones. The defect of gallbladder muscle after
cholesterol feeding and stones might reside in the steps before
G protein activation.