Effect of basal lamina of ovarian follicle on T- and L-type Ca(2+) currents in differentiated granulosa cells.

Patch clamp experiments were conducted to study the effects of basal lamina (basement membrane) of chicken ovarian follicle on membrane Ca(2+) currents in differentiated chicken granulosa cells in a homologous system. The whole cell patch clamp technique was used to simultaneously monitor membrane capacitance (an indirect measure of total cell surface area) and currents flowing through voltage-dependent Ca(2+) channels (using Ba(2+) as the charge carrier). Membrane capacitance was smaller in cells incubated on intact basal lamina than in control cells (incubated on tissue culture-treated plastic substratum). Granulosa cells expressed both T- and L-type Ca(2+) currents, and the amplitudes of the currents in cells incubated on intact basal lamina were significantly lower than those of control cells. Also, granulosa cells incubated on intact basal lamina were found to have significantly lower T- or L-type Ca(2+) current densities than control cells. Intact basal lamina that had been stored for 12 mo produced effects on T- and L-type Ca(2+) currents similar to those caused by freshly isolated basal lamina. The basal lamina was solubilized completely in one step and used to coat glass coverslips (uncoated glass coverslips served as controls). Granulosa cells incubated on coverslips precoated with solubilized basal lamina assumed spherical shape similar to those incubated on intact basal lamina. Similar to the observations made for intact basal lamina, the solubilized basal lamina suppressed T- and L-type Ca(2+) currents in the differentiated granulosa cells. Moreover, fibronectin, laminin, and type IV collagen, obtained from commercial sources, attenuated T- and L-type Ca(2+) currents in the differentiated granulosa cells. This interplay between basal lamina and Ca(2+) currents may be one mechanism that subserves the effects of the matrix material on metabolic functions of granulosa cells.