Suppression of the carbachol-activated nonselective cationic current by antibody against alpha subunit of G(o) protein in guinea-pig gastric myocytes

In this study, we investigated which subtype of GTP-binding protein (G protein) is related to muscarinic activation of nonselective cation (NSC) channels in gastric smooth muscle. Inward cationic current was activated by the application of 50 pM carbachol (I(CCh)) at a holding potential of -60 mV with the same CsCl-rich solution in both pipette and bath. The same cationic current as I(CCh) was slowly activated by the dialysis of guanosine 5'-O-(3- thiotriphosphate) (GTP[γ-S]) through the pipette. Since it is known that pertussis toxin pretreatment can block I(CCh), antibodies (Abs) against G(α,i) (anti-G(α,i)) or G(α,o) (anti-G(α,o)) were tested. Activation of I(CCh) was blocked by the addition of anti-G(α,o). However, anti-G(α,i) Abs had no significant effect on I(CCh). The expression of G(α,o) in guinea-pig gastric smooth muscle was confirmed by Western immunoblot analysis. These results suggest that G(o)-type protein may mediate signals from the muscarinic receptor to NSC channel in guinea-pig gastric myocytes.