Cation-permeable vacuolar channels in the tonoplast of Marchantia polymorpha

The object of our patch-clamp study was the liverwort Marchantia polymorpha. Basic solutions were symmetrical in the bath and in the pipette and contained 100 mM KCl and 0.5 mM CaCl sub(2). Whole vacuole recordings mainly showed slowly activating outward rectifying currents, typical for SV (slow-vacuolar) channels. The unitary conductance registered from isolated patches was 74.7+ or -4.0 pS at 100 mV. Replacement of K with Na+ caused reduction of the unitary conductance to 59.8+ or -6.87 pS. Tenfold decrease of the KCl shifted the reversal potential close to E sub(k) and caused reduction of the SV unitary conductance to 31.5+ or -5.5 pS. Moreover, the gradient of KCl revealed the current at the negative potential; the unitary conductance at -100 mV was 43.3+ or -0.5 pS, whereas the gradient of Na+ did not evoke such an effect. This may suggest that inwardly rectifying K channels exist in the tonoplast of the liverwort.