ACTIVATION OF PROTEIN-KINASE-A AND PROTEIN-KINASE-C MEDIATES THE DEPOLARIZING EFFECT OF LH IN OVINE CUMULUS-CORONA CELLS

We have studied the changes in membrane potential induced by LH in cum ulus and granulosa cells isolated from sheep antral follicles. The inv estigation was earned out by using a non-invasive technique based oil the use of a membrane potential sensitive probe, bis-oxonol. The membr ane potential of mural granulosa cells was totally unaffected by LH, w hile that of cumulus or corona cells showed a marked depolarisation, s tarting 2-3 min after the addition of the hormone and plateauing after 5-10 min. None of the cells tested reacted to FSH. In the second part of the experiment the role of protein kinase A (PKA) and protein kina se C (PKC) in mediating the effect of LH was studied. The selective ac tivation of PKA or PKC induced in cumulus-corona cells a rapid hyperpo larisation due re, increased Cl and K conductance respectively. By con trast, the simultaneous activation of the two kinases induced a rapid membrane depolarisation due to the progressive decrease in It conducta nce. The activation of each kinase or their combined stimulation did n ot induce any change ill the membrane potential of mural granulosa cel ls. These data demonstrated that LH has a depolarising effect regional ly circumscribed to cumulus-corona cells and that this depolarisation depends on a reduction of K conductance caused by the activation of PK A and PKC.