Calcium currents and GABAB receptors in the dorsal sensory cells of the lamprey spinal cord

Patch-clamp studies were performed on the isolated dorsal sensory cells of the spinal cords of three species of lamprey,Ichthyomyzon unicuspis, Petromyzon marinus, andLampetra fluviatilis, to measure changes in the amplitudes of calcium current induced by GABA and its specific antagonists and agonists. The experiments showed that GABA (4 mM) reduced the peak amplitude of the calcium current by 28.5±4.9%, with subsequent recovery to 96.2±9.2% of control (n=45). The GABA_B agonist baclofen had similar effects. The GABA_A agonists glycine and taurine had no effect on the Ca²⁺ current. The inhibitory effect of GABA was blocked by 2-hydroxysaclofen (a GABA_B antagonist), but persisted in the presence of bicuculline (a GABA_A antagonist). These results are evidence that the membranes of dorsal sensory cells contain GABA_B receptors, which significantly increases our under-standing of the mechanisms of presynaptic inhibition in the spinal cords of the cyclostomata. Translated from Rossiiskii Fiziologischeskii Zhurnal imeni I. M. Sechenova, Vol. 83, No. 11-12, pp. 79–91, November–December, 1997.