Inhibitory effect of phorbol 12,13 dibutyrate on carbachol-activated nonselective cationic current in guinea-pig gastric myocytes

The effect of protein kinase C (PKC) on carbachol (CCh)-activated nonselective cationic current (I-CCh) Was investigated in guinea-pig gastric myocytes using a PKC activator, phorbol 12, 13 dibutyrate (PDBu). Pretreatment with 1 mu M PDBu suppressed I-CCh by 96.5 +/- 2.9% (n = 14) in a reversible manner in nystatin-perforated mode. In the presence of 1 mu M chelerythrine , a PKC inhibitor, inhibition of I-CCh by PDBu was not seen. In whole-cell mode, the inhibition of I-CCh by PDBu was dependent on intracellular MgATP. In the presence of MgATP in the pipette, PDBu decreased I-CCh by 98.8 +/- 1.2% (n = 5) as was observed in nystatin-perforated mode. However, PDBu had little effect on I-CCh in the absence of MgATP in the pipette; the extent of inhibition was 12.7 +/- 4.3% (n = 8). PDBu also suppressed the generation of cationic current induced by intracellularly perfused GTP[gamma S]. In the PDBu-pretreated group (n = 9) and PDBu-untreated control group (n = 6), GTP[gamma S]-induced currents were 6.7 +/- 2.4 pA and 236 +/- 23 pA, respectively. These results suggest that PKC modulates I-CCh at postreceptor sites via protein phosphorylation.