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The aim of this study was to evaluate the effect of pertussis toxin (PTX) on the depolarising component of the action of FSH on the membrane potential of Sertoli cells, which is linked to the rapid entry of Ca2+ into cells and to the Ca2+-dependent transport of neutral amino acids by the A system. This model allowed us to analyse the involvement of Gi proteins in the action of FSH in these phenomena. In parallel, using an inactive analogue of IGF-1, JB1, and an anti-IGF-I antibody we investigated the possible mediating role of IGF-I on these effects of FSH because IGF-I is produced and released by testicular cells in response to stimulation by FSH and shows depolarisation effects on membrane potential similar to those from FSH. Our results have the following implications: a) the rapid membrane actions of FSH, which occur in a time-frame of seconds to min and include the depolarisation of the membrane potential, and stimulation of 45Ca2+ uptake and [14C]- methyl aminoisobutyric acid ([14C]-MeAIB) transport, are nullified by the action of PTX and, therefore, are probably mediated by GiPCR activation; b) the effects of FSH were also nullified by verapamil, an L-type voltage-dependent Ca2+ channel blocker; c) wortmannin, an inhibitor of PI3K, prevented FSH stimulation of 45Ca2+ entry and [14C]-MeAIB transport; and d) these FSH actions are independent of the IGF-I effects. In conclusion, these results strongly suggest that the rapid action of FSH on L-type Ca2+ channel activity in Sertoli cells from 10- to 12-day-old rats is mediated by the Gi/βγ/PI3Kγ pathway, independent of the effects of IGF-I. |
