MODULATION OF HYBRID BASS RETINAL GAP JUNCTIONAL CHANNEL GATING BY NITRIC-OXIDE

1. To elucidate the role of the nitric oxide (NO) transmitter system i n the regulation of gap junctional channel gating, we have examined th e effects of the NO donor sodium nitroprusside (SNP) on the electrical synapses of hybrid bass H2-type horizontal cells. 2. SNP reversibly r educed the macroscopic junctional conductance without significantly ch anging voltage sensitivity. 3. Kinetic analyses showed that SNP made t he voltage-dependent decay of junctional currents more rapid. 4. Singl e-channel data showed that SNP reduced channel open probability by red ucing channel open frequency. 5. The action of SNP can be prevented or largely reduced by the NO scavenger, haemoglobin. NO release by SNP s olutions was detected directly by a NO sensor.6. NO appears to modulat e the gap junctional conductance by activating the cGMP-cGMP-dependent protein kinase G (PKG) pathway. A membrane-permeable cGMP analogue, 8 -Br-cGMP, mimics the action of SNP. A soluble guanylate cyclase inhibi tor (LY-83583) and a highly specific cGMP-dependent protein kinase inh ibitor (RKRARKE) blocked the action of NO. 3-Isobutyl-1-methylxanthine (IBMX), a non-specific phosphodiesterase inhibitor, potentiated the e ffect of SNP. 7. [Ca2+](i) image studies showed that NO donors did not change [Ca2+](i) in horizontal cells, suggesting that the regulation of junctional channels by NO is [Ca2+](i) independent.