Abstract
In the present study we investigated the possible existence of a Na+/Ca2+ exchange mechanism in the basolateral membrane of the frog skin epithelium and whether such a mechanism plays a role in the regulation of transepithelial Na+ transport. Cytosolic calcium ([Ca2+]i) was measured with the probe fura-2 in a set-up in which pieces of tissue were mounted on the stage of an epifluorescence microscope. Na+ transport was measured as the amiloride-sensitive short-circuit current (Isc) using a conventional voltage clamp. Basal [Ca2+]i was 65+/-6 nM (n=15). Removal of Na+ from the mucosal solution had no effect on [Ca2+]i. When Na+ was removed from the serosal solution, [Ca2+]i increased biphasically to a peak of 220+/-38 nM (n=8, P=0.006). Readdition of Na+ to the serosal solution returned [Ca2+]i to control level. The serosal Na+ gradient and changes in [Ca2+]i were closely correlated; stepwise changes in serosal Na+ were followed by stepwise changes in [Ca2+]i. These observations indicate the existence of a Na+/Ca2+ exchange mechanism in the basolateral membrane of the frog skin epithelium. The transepithelial Na+ transport decreased from 13.2+/-1.8 to 9.2+/-1.5 microA cm-2 (n=8, P=0.049) when Na+ was omitted from the serosal solution. When this protocol was repeated in the absence of serosal Ca2+, Na+ transport decreased similarly from 16.7+/-1.7 to 11.6 +/-1. 8 microA cm-2 (n=6, P=0.004). We conclude that it is unlikely that the observed decrease in Isc after removal of serosal Na+ is due to an increase in [Ca2+]i per se.
| Original language | English |
|---|---|
| Journal | Pflügers Archiv - European Journal of Physiology |
| Volume | 437 |
| Issue number | 2 |
| Pages (from-to) | 175-81 |
| Number of pages | 7 |
| ISSN | 0031-6768 |
| Publication status | Published - 1999 |
Keywords
- Algorithms
- Animals
- Biological Transport
- Calcium
- Cytosol
- Enzyme Inhibitors
- Epithelium
- Extracellular Space
- Female
- Rana temporaria
- Skin
- Sodium
- Thapsigargin