The prolactin-producing rat anterior pituitary GH4C1 cells possess Ca2+-activated K channels which are activated by physiological elevations of the cytosolic Ca2+ concentration even at membrane potentials more negative than the normal level of about -50 mV. Whole-cell current recordings showed a marked outward tail current following depolarizing voltage steps to 0 mV from a holding potential close to the normal membrane potential. The half-time of this tail current was about 1.3 s after a 4-s depolarization step. The GH4C1 cells also possess voltage-activated Ca channels, and we conclude that this tail current is a Ca2+-activated K+ current for the following reasons: (1) The reversal potential for the tail current was close to the K+ equilibrium potential for a range of transmembrane K+ gradients. (2) The tail current was blocked by a Ca2+ antagonist, and the voltage dependence of this current closely mirrored the voltage dependence of the isolated Ca2+ current. The time-course of the decline of the tail current thus reflects the removal rate of the Ca2+ entering the cytosol through voltage-dependent Ca channels during the depolarizing voltage step. VIP stimulates prolactin secretion from GH4C1 cells, and this peptide prolonged the half-time of the tail current by about 47% in 63% of the cells. This indicates that VIP may prolong the transient cytosolic Ca2+ elevations following the action potentials in these cells. Such a mechanism might be an important factor for the control of the cytosolic Ca2+ level, and hence hormone secretion.

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Mutations in dysferlin cause Limb-Girdle and Miyoshi Muscular Dystrophy. Dysferlin is structurally related to Otoferlin, a protein involved in the calcium triggered release of neurotransmitters in cochlear hair cells. Dysferlin is a calcium-binding protein with a single membrane-spanning domain thought to be required for membrane wound repair. The specific function that dysferlin performs in wound healing is unknown. Here we report the activation of an intercellular signaling pathway in sea urchin embryos by membrane wounding that evokes calcium spikes in neighboring cells. This pathway was mimicked by ATP application, and inhibited by apyrase, cadmium, and omega-agatoxin IVA. Microinjection of dysferlin antisense morpholinos blocked this pathway; control morpholinos did not. Co-injection of mRNA encoding human dysferlin with the inhibitory morpholino rescued signaling activity. Our results indicate that membrane wounding triggers membrane depolarization, calcium influx through an agatoxin sensitive voltage-gated calcium channel, and ultimately the secretion of ATP. Moreover, dysferlin appears to mediate one of the essential steps in this signaling cascade.

The p‐substituted 4‐chlorobutyro(valero)phenones (I) react with antimony pentachloride (II) to give the dihydrofurylium hexachloroantimonates (III).