Effect of melittin on PD, resistance and short-circuit current in the frog gastric mucosa.
In an in-vitro preparation of gastric mucosae of Rana pipiens, the effect of adding melittin to a concentration of 5x10-6 M in the secretory solution on the transepithelial potential difference (PD), resistance (R) and short-circuit current (Isc) was studied. In 20 min, melittin decreased the PD by 9.3 mV and R by 148 ohm cm2. These changes can be explained by a decrease in the resistance, RP, of the paracellular pathway. To determine whether specific-ion pathways were responsible for the decrease in R, the effect of melittin on the partial conductances of Cl-, K+ and Na+ was also studied using the ion substitution method. Melittin decreased the PD response to changes in nutrient Na+, K+ and Cl- and the PD response to changes in secretory Cl-, but did not affect PD responses to changes in secretory Na+ or K+. Therefore, melittin decreased the nutrient membrane partial conductances of Cl-, K+ and Na+ and secretory membrane partial conductance of Cl-, without affecting the secretory partial conductances of Na+ or K+. Initially, melittin increased Isc in regular and Cl--free but not in Na+-free solutions. There was a delayed decrease in Isc. The results indicate that melittin decreases RP, increases the Na+ conductance of the secretory membrane and inhibits, eventually, the Na+/K+-ATPase pump.
Carrasquer
G
G
Department of Medicine, Division of Nephrology, University of Louisville, Louisville, KY 40292, USA.
Li
M
M
Yang
S
S
Schwartz
M
M
D000818:Animals; D002712:Chlorides; D003470:Culture Media; D005753:Gastric Mucosa / Q000187:drug effects* / Q000502:physiology; D008555:Melitten / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects*; D011188:Potassium; D011894:Rana pipiens; D012964:Sodium
D002712:Chlorides; D003470:Culture Media; D008555:Melitten; D012964:Sodium; D011188:Potassium