Carbachol-induced sodium current in guinea pig ventricular myocytes is not regulated by guanine nucleotides.
Muscarinic (M2) receptor occupancy by carbachol induces a tetrodotoxin- and pertussis toxin-resistant Na+ current which underlies its positive inotropic effect in guinea pig ventricular cells. We tested the effect of activating [GTP gamma S, Gpp(NH)p] and inactivating (GDP beta S) guanine nucleotides on this carbachol-induced current because guanine nucleotide binding proteins are reported to transduce the effect of muscarinic agonist. A whole-cell voltage clamp method was used. The carbachol (300 microM)-induced current was not significantly changed at any membrane voltage in the absence and the presence of 10 microM GTP gamma S, 100 microM Gpp(NH)p or 500 microM GDP beta S in the patch pipette (inward current amplitude at -80 mV: -21 +/- 1.5 pA, control; -22 +/- 1.3 pA, GTP gamma S; -20, -16 pA, Gpp(NH)p; -20 +/- 2.3 pA, GDP beta S; n = 31, 11, 2 and 14, respectively). The current amplitude was not affected by prolonged dialysis (120 min) of the cell with Gpp(NH)p and/or by the presence of greater concentrations of guanine nucleotides. On the other hand, 10 microM GTP gamma S directly activated the muscarinic K+ channel current within 60 sec after patch rupture in atrial myocytes; either GTP gamma S or GDP beta S (500 microM) occluded activation of this current by carbachol. When isoproterenol had increased L-type Ca++ current in ventricular myocytes, carbachol-induced inhibition of this current was suppressed when GTP gamma S (10 microM) was present in the pipette solution. Therefore, myocytes were dialyzed with effective concentrations of guanine nucleotides.(ABSTRACT TRUNCATED AT 250 WORDS)
Shirayama
T
T
Department of Pharmacology, University of Connecticut Health Center, Farmington.
Matsumoto
K
K
Pappano
A J
AJ
D000818:Animals; D002217:Carbachol / Q000494:pharmacology*; D003956:Dialysis; D006150:Guanine Nucleotides / Q000378:metabolism*; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects*; D066298:In Vitro Techniques; D008564:Membrane Potentials; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction; D015222:Sodium Channels / Q000187:drug effects* / Q000502:physiology; D016276:Ventricular Function
D006150:Guanine Nucleotides; D011976:Receptors, Muscarinic; D015222:Sodium Channels; D002217:Carbachol