dc.description.abstract | We investigated the transepithelial potential
(TEP) and its responses to changes in the external medium in
Alcolapia grahami, a small cichlid fish living in Lake
Magadi, Kenya. Magadi water is extremely alkaline
(pH = 9.92) and otherwise unusual: titratable alkalinity
(290 mequiv L-1, i.e. HCO3
- and CO3 2-) rather than Cl-
(112 mmol L-1) represents the major anion matching
Na? = 356 mmol L-1, with very low concentrations of
Ca2? and Mg2? (\1 mmol L-1). Immediately after fish
capture, TEP was ?4 mV (inside positive), but stabilized at
?7 mV at 10–30 h post-capture when experiments were
performed in Magadi water. Transfer to 250% Magadi water
increased the TEP to ?9.5 mV, and transfer to fresh water
and deionized water decreased the TEP to-13 and-28 mV,
respectively, effects which were not due to changes in pH or
osmolality. | en |