Susumu Fujisawa and Toshihiko Iijima*
Department of Pharmacology, Akita University School of Medicine, Akita
010 - 8543, Japan
(*) To whom correspondence should be addressed.
Abstract: Arginine vasopressin (AVP) (0.03 - 3 ƒÊM) produced
transient negative responses that were followed by slowly developing positive
inotropic responses in guinea pig papillary muscles. The inotropic responses
were antagonized by OPC-21268 (10 ƒÊM), but not by OPC-31260, and suppressed
by neomycin (3 mM). The negative inotropic response was hardly affected
by staurosporine (10 nM) and H-7 (10 ƒÊM). AVP (1 ƒÊM) elicited a transient
decrease followed by a slowly developing increase in ICa. The
latter increase in ICa was not elicited in the presence of staurosporine
(1 nM). These results indicate that AVP stimulates V1 receptors that couple
to phosphoinositide hydrolysis and thereby increases intracellular Ca2+
and activates protein kinase C.
Keywords: Vasopressin-1 receptor, Protein kinase C, L-type Ca2+
current