[The role of protein kinase C-mediated phosphorylation of type III inositol 1, 4, 5-triphosphate receptor in cholecystokinin octapeptide induced calcium mobilization in gastric antral smooth muscle cells].

OBJECTIVE: To study the effects of sulfated cholecystokinin octapeptide (sCCK-8S) on intracellular calcium release and extracellular calcium influx in gastric antral smooth muscle cells (SMC) and the mechanism thereof.

METHODS: (1) Longitudinal muscle (LM) and circular muscle (CM) strips of gastric antrum and pylorus were isolated from SD rats and suspended in a tissue chamber to record the contractile responses by polyphysiography. (2) Immunoprecipitation, electrophoresis, and immunoblotting were used to detect the phosphorylation of type III inositol 1, 4, 5-triphosphate receptor (InsP(3)R(3)) in the SMCs. (3) The responsiveness of gastric SMC to CCK-8S was examined by using fura-2-loaded microfluorimetric measurement of intracellular calcium concentration ([Ca(2+)]i). (4) The current of L-type calcium channels (ICaL) was recorded by using patch-clamp techniques.

RESULTS: (1) Significant changes to CCK-8S were found in the mean contractile amplitude of the CM and frequency of LM of gastric antrum and could be suppressed by CCK-A receptor (CCK-AR) antagonist and ATPase inhibitors. (2) CCK-8S stimulation of SMC resulted in PKC-dependent phosphorylation of the InsP(3)R(3). (3) CCK-8S-evoked significant increase in [Ca(2+)]i [from (69 +/- 7) mol/L to (472 +/- 36) nmol/L, P < 0.01] could be suppressed by CCK-AR antagonist, ATPase inhibitors and protein kinase C (PKC) activator; whereas on condition that extracellular calcium was removed or L-type calcium inhibitor nifedipine was added a small but significant increase of [Ca(2+)]i could be still elicited by CCK-8S. (4) CCK-8S-intensified calcium current [from (-56 +/- 7) pA to (-89 +/- 6) pA, P < 0.01] could be apparently inhibited by respective administration of nifedipine, ATPase inhibitors, and calcium dependent chloride channel (I(Cl-Ca)) blocker (all P < 0.01).

CONCLUSION: CCK-8S-evoked [Ca(2+)]i increase in gastric antral SMCs depends on the release of intracellular calcium stores, which is regulated by PKC mediated phosphorylation of InsP(3)R(3). The released intracellular calcium in turn activates the L-type voltage-dependent calcium channels (VDCC) through the activation of calcium dependent chloride channels, and ultimately results in the occurrence of contraction response of smooth muscles.