Tetrodotoxin blocks
A i.e. y Na+ during action potentialInhibitors & toxinsSodium dependent glucose transpoer (SGLT or Na+ glucose co transpoer) is inhibited by phlorizinQ whereas, phloretin inhibits sodium (Na+) independent glucose transpoer (GLUT 2) in intestineQ.Fish neurotoxin tetrodotoxin (applied externally) block Na' channelsQ (esp early membrane voltage dependent Na' current; hence 'm' gates controlling Na' channels externally) where as enzyme pronase (applied internally) block voltage dependent inactivation of Na* current (hence 'h.' gates controlling Na' channels from inside).Tetraethyl ammonium or 4 aminopyridine block potassium channelQ (esp delyed voltage dependent increase in K* permeability and hence 'n' gate).Absorption of Hexose in intestineHexoses are rapidly and completely absorbed before the meal reach terminal ileumTranspo of most hexoses (glucose & galactose) is dependent on Na' ions in intestinal lumen; a high Na' concentration facilitates and a low concenteration inhibits sugar influx into the epithelial cells.This is because Na' & glucose share a same cotranspoer or sympo, the sodium dependent glucose transmpoer (SGLT), Na' glucose cntranspoer). These (SGLT 1 & 2) resemble glucose transpoers responsible for facilitated diffusion in that they cross cell membrane 12 times and have their - COOH & - NH2 terminals on cytoplasmic side of membrane. However , there is no homology to glucose transpoer (GLUT). SGLT- 1 is responsible for uptake of dietary glucose from gut where as SGLT-2 is responsible for glucose transpo out of renal tubules.
yNa+ during action potential
yK+ during action potential
yNa+ during resting state
yK+ during resting state