Effects of forskolin on the longitudinal internal resistance (ri) in rabbit sinus node strips

The effect of several concentrations of 7-0-hemisuccinyl, 7-deacetyl forskolin on ri was studied by means of microelectrode and single sucrose gap techniques. Twenty mumol.l-1 of forskolin added to the sucrose gap lowered ri by 15% below the control value. The drug applied at 50 mumol.l-1 initially decreased ri by 31%, and then it increased the resistance by 43% above the control value. The possible mechanisms underlying these effects are discussed in terms of cAMP and Ca action on the cell coupling.