Novel Cl- currents elicited by follicle stimulating hormone and acetylcholine in follicle-enclosed Xenopus oocytes.

Abstract

Voltage-clamp techniques were used to study the membrane currents elicited by follicle stimulating hormone (FSH) and acetylcholine (ACh) in follicleenclosed oocytes of Xenopus laevis (follides). Both agonists caused complex responses that were more evident when the follicles were in hypotonic Ringer solution (HR; 190.4 mosM). In this medium, currents activated by FSH regularly showed three phases whereas currents activated by ACh displayed three to six phases. At a holding potential of -60 mV, FSH, and ACh responses involved combinations of inward and outward currents. Both FSH and ACh responses included a slow smooth inward component that was associated with an increase in membrane conductance, mainly to C1-(Sin)-This current was strongly dependent on the osmolarity of the external solution: an increase in osmolarity of the HR solution of 18-20 mosM caused a 50% decrease in Sin. In contrast, a fast and transient C1-current (Fin) specifically elicited by ACh was not dependent on osmolarity. Both, Fin and Sin currents required the presence of follicular cells, since defolliculation using three different methods abolished all the response to FSH and at least four components of the ACh responses, The membrane channels carrying Fin and oscillatory CIcurrents elicited by stimulation of ACh or serum receptors, were much more permeable to I-and Br-than CI-, whereas Sm channels were equally permeable to these anions. Unlike the oscillatory CI-currents generated in the oocyte itself, Sin and Fin currents in follicle-enclosed oocytes were not abolished by chelation of intracellular Ca 2+, either with EGTA or BAPTA, which suggests that intracellular Ca 2+ does not play a critical role in the activation of these currents. Our experiments show that Si, and Fin currents are quite distinct from the previously characterized oscillatory C1-responses of oocytes. Moreover, the results strongly suggest that the FSH and ACh receptors, the CI-channels mediating the Fin and Sin currents, together with the necessary elements for their activation, are all located in the follicular cells and not in the oocyte.Many aspects of follicular cell physiology in Xenopus laevis, and other species, are regulated by hormones and neurotransmitters, including FSH and ACh. The follicular CI-currents described in this paper may play an important role in the follicular cell-oocyte development.

Ionic Currents Activated via Purinergic Receptors in the Cumulus Cell-Enclosed Mouse Oocyte1

“…It is expected that if this coupling is strong enough, a CEO would behave as an isopotential cellular aggregate, and would be amenable to recording using the two-electrode voltage clamp technique, as has been shown for other cell aggregates such as cardiomyocytes, acinar cells, and Xenopus follicles [14,[32][33][34][35][36].…”

Functional interaction between native G protein-coupled purinergic receptors in Xenopus follicles

“…and as e.t.r., where the inner epithelium of the follicle, together with theca and blood vessels, was separated using sharp forceps (2,9), leaving the follicular cell layer protected by its basement membrane (1,13). Typically, the w.f.…”

“…follicles to study the effect of epithelium and theca removal on I K,cAMP and F Cl elicited by Ado or ATP. As control responses, the same follicles were also tested for acetylcholine (ACh), an agonist that operates the F Cl channels and inhibits I K,cAMP in a manner similar to ATP (9,19). Fig.…”

“…Three main subtypes have been described: (i) A2 receptors responsive to Adenosine (Ado), coupled to cAMP synthesis and opening of K ϩ channels (cAMP-dependent K ϩ current, I K,cAMP ), that are sensitive to glibenclamide (3-7); (ii) P2Y receptors responsive to ATP and UTP that operate Cl Ϫ channels generating fast and slow Ca 2ϩ -independent currents (F Cl and S Cl ) (2,8,9); and (iii) a purinergic receptor, referred to as a P3 or novel P1 receptor, that is sensitive to both Ado and ATP and coupled to I K,cAMP generation (10,11). Also, there is a P2Y receptor that inhibits I K,cAMP and is probably the same as the receptor involved in F Cl and S Cl activation (2,12,13).…”

Chronic fatigue syndrome is an acquired neurological channelopathy

“…These changes reduce available neuronal ACh and depress cholinergic neurotransmission following stress that could lead to a state of postsynaptic cholinergic receptor upregulation and delayed cholinergic supersensitivity. Since ACh is a receptor speci®c agonist that opens membrane Cl À channels (Artellano and Miledi, 1993;Ikeda et al, 1995), supersensitivity to ACh in CFS (and syndrome X) would induce secondary changes in Cl À ion channel functions. Drugs that block Cl À channels, e.g.…”