Electrogenic action of calcium on crayfish gill

✍ Scribed by L. B. Kirschner

• Publisher: Springer-Verlag
• Year: 1994
• Tongue: English
• Weight: 661 KB
• Volume: 164
• Category: Article
• ISSN: 0174-1578
• DOI: 10.1007/bf00354082

✦ Synopsis

When intact crayfish are in an ion-poor medium (KC1, 0.1 mmol.1-1 + KHCO3, 0.1 mmol.1-1) there is a large potential difference (transepithelial potential difference), -20 to -40 mV (hemolymph negative), across the gills. Addition of Ca 2+ to the medium is followed by a rapid change in transepithelial potential difference to near 0 inV. The transepithelial potential difference showed a non-linear dependence on [Ca2+]o,t with a limiting value of +2 to + 10 mV at > 1 mmol.1-1. The concentration generating a half-maximum transepithelial potential difference change (15-20mV) was 0.1 to 0.2 mmol. 1-1. Three other alkaline earth ions were also electrogenic; Ba 2--caused slightly larger transepithelial potential difference changes, Sr 2+ and Mg 2+ were a little less effective. It has been suggested that the transepithelial potential difference in ion-poor medium (in fish) is due to the diffusive efflux of NaCI across the gills, with a C1-/Na + permeability ratio of < 1. Evidence is presented that this might be the case in crayfish. The electrogenic effect of Ca 2 § might then be due to its effect on gill permeability to Na + and CI-such that the permeability ratio increased and approached unity as the transepithelial potential difference approached 0. However, this was shown to be unlikely. An alternative explanation for Ca 2 § dependence of the transepithelial potential difference is that active inward Ca 2+ transport is electrogenic.