Agonist-independent modulation of L-type Ca currents by basal Gs protein activities in single guinea pig ventricular myocytes.
The modulation of L-type Ca2+ currents (I(Ca,L)) by the basal activities of G proteins was studied in adult guinea pig ventricular myocytes by whole-cell patch-clamp techniques. With intrapipette guanosine triphosphate (GTP) (100 microM), a specific inhibition of G1 proteins by pertussis toxin (PTX) produced an increase in the basal density of I(Ca,L) (from 11.0+/-0.8, n = 13, to 25.0+/-2.0 pA/pF, n = 11, at OmV test potential). In addition, PTX shifted the forskolin (Fsk) concentration-I(Ca,L) response relation significantly leftward (EC50, = 63.7+/-12.5 vs 625+/-75 nM). With intrapipette guanosine diphosphate (GDP)betaS (1 mM), the Fsk-I(Ca,L) relation was also shifted leftward (EC50 = 197+/-18.3 vs 781+/-82.5 nM). However, chronic GDPbetaS dialysis accelerated the rundown of I(Ca,L) significantly, suggesting a potential contribution of Gs proteins in maintaining basal I(Ca,L). In contrast, intra-pipette GTPgammaS (100 microM) produced a transient rise in I(Ca,L) from 11.0+/-3.0 to 22.8+/-7.0 pA/pF (in 3.4 min after whole-cell formation at 0 mV, n = 9), presumably through the activation of Gs proteins. It was followed by a gradual decline in I(Ca,L) (to 15.5+/-3.5 pA/pF), which was still enhanced by Fsk (EC50 = 1450+/-98 nM), indicating that the current decay was not solely due to rundown but to activation of Gi proteins. Gs, in addition to Gi proteins, show sufficient basal activity to modulate I(Ca,L) in an agonist-independent manner.
Makita
T
T
Department of Cardiovascular Medicine, Kyoto University Graduate School of Medicine, Japan.
Horie
M
M
Xie
L H
LH
Okada
Y
Y
Sasayama
S
S
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002120:Calcium Channel Agonists / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D005576:Colforsin / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000166:cytology* / Q000378:metabolism*; D066298:In Vitro Techniques; D018408:Patch-Clamp Techniques; D037342:Pertussis Toxin; D010566:Virulence Factors, Bordetella / Q000378:metabolism
D002120:Calcium Channel Agonists; D020746:Calcium Channels, L-Type; D010566:Virulence Factors, Bordetella; D005576:Colforsin; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases