Effects of Ca++ depletion on lens equatorial currents in frog lenses

The combination of the vibrating probe measuring the outward equatorial current (J) with microelectrodes measuring PD and the response to injected current provides one of the best means of relating macro findings of lens currents to the micro data that have been reported using the patch clamp technique. In standard frog Ringers solution the equatorial current appears to be a relatively pure K+ current with a reversal potential of -95 mV. This agrees with the reversal potential of the 45 pS K+ channel. When Ca++ is removed from the medium bathing the lens the input resistance (R) decreases, the PD becomes less negative and the current J increases. This process can be reversed by adding Ca++ or Mn++ to the Ca++ deficient medium. When all Ca++ is removed from the medium by adding EGTA in the absence of Ca++, the increase in J is less than expected. However, if Na+ is replaced by TMA in the Ca++ depleted EGTA medium the current is seven times as great. These changes are consistent with those found in non-selective cation channels in the absence of Ca++.