ABSTRACT
Administration of gamma-2-melanocyte stimulating hormone (gamma-2-MSH) to rats increases blood pressure, heart rate and natriuresis by acting through the nervous system and this response is more pronounced in spontaneous hypertensive rat (SHR). The molecular mechanisms underlying these effects are unknown, however, protein kinase C (PKC) activity is higher in SHR tissues and melanocortins are known to activate the phosphoinositide (PI) signaling pathway. In this study, we tested the hypothesis that gamma-2-MSH potentiation of PKC activation is increased in nerve terminals from SHR brain. Synaptosomes were isolated from SHR and age-matched control Wistar Kyoto (WKY) rats and incubated with gamma-2-MSH. Total particulate-fraction associated PKC activity was determined and the expression of individual isozymes analyzed by immunoblotting. Treatment with gamma-2-MSH resulted in an increase in particulate-associated PKC activity in hindbrain synaptosomes that was more prominent in SHR. The levels of membrane-associated PKC-alpha and beta-isozymes were considerably less than for PKC-gamma in these tissues as determined by immunoblotting. The novel PKC isozymes delta and epsilon were detected in total synaptosomes but not in membrane fractions. These data suggest that PKC-gamma is the major presynaptic PKC isozyme and that PKC may be an important mediator for gamma-2-MSH in neural tissues.
