The role of a PDGF-activated nonselective cation channel in the proliferative response

Hydrostatic pressure-regulated ion transport in bladder uroepithelium

The effect of hydrostatic pressure on ion transport in the bladder uroepithelium was investigated. Isolated rabbit uroepithelium was mounted in modified Ussing chambers and mechanically stimulated by applying hydrostatic pressure across the mucosa. Increased hydrostatic pressure led to increased mucosal-to-serosal Na+ absorption across the uroepithelium via the amiloride-sensitive epithelial Na+ channel. In addition to this previously characterized pathway for Na+ absorption, hydrostatic pressure also induced the secretion of Cl- and K+ into the mucosal bathing solution under short-circuit conditions, which was confirmed by a net serosal-to-mucosal flux of 36Cl- and 86Rb+. K+ secretion was likely via a stretch-activated nonselective cation channel sensitive to 100 microM amiloride, 10 mM tetraethylammonium, 3 mM Ba2+, and 1 mM Gd3+. Hydrostatic pressure-induced ion transport in the uroepithelium may play important roles in electrolyte homeostasis, volume regulation, and mechanosensory transduction.

Ionic currents underlying developmental regulation of repetitive firing in Aplysia bag cell neurons

We have investigated the developmental regulation of the ability to fire repetitively in the bag cell neurons of Aplysia californica, a neuronal system in which the behavioral effects of repetitive firing are well characterized. Adult bag cell neurons exhibit an afterdischarge, consisting of prolonged depolarization and repetitive firing, which causes the release of several peptides from these neurons that induce egg-laying behaviors. Afterdischarge can be triggered in vitro by a variety of stimuli, including electrical stimulation and exposure to the potassium channel blocker tetraethyl ammonium chloride (TEA). In contrast to adults, juvenile neurons did not exhibit afterdischarge in response to pleural-abdominal connective shock or TEA. Juvenile neurons did exhibit, however, prolonged depolarizations in the presence of TEA, perhaps reflecting the anlage of the mechanism responsible for afterdischarge in the adult. To investigate developmental mechanisms underlying the regulation of repetitive firing, we compared ionic currents in adult and juvenile bag cell neurons. We found that during the period in which these neurons acquire the capacity to fire repetitively, a number of currents are regulated: (1) three K+ currents decrease (Ca2+)-dependent K+ and two components of voltage-dependent delayed-rectifier K+ current); (2) A-type K+ current increases; and (3) two Ca2+ currents increase (basal and PKC-activated). This pattern is consistent with the increase in the ability to fire repetitively that we observe during maturation: our results indicate that developmental control of repetitive firing in this system is accompanied by selective regulation of specific ionic currents which, after maturation, play important roles in generating the afterdischarge and triggering egg-laying behaviors.