Electrophysiological study of Drosophila rhodopsin mutants.

Electrophysiological investigations were carried out on several independently isolated mutants of the ninaE gene, which encodes opsin in R1-6 photoreceptors, and a mutant of the ninaD gene, which is probably important in the formation of the rhodopsin chromophore. In these mutants, the rhodopsin content in R1-6 photoreceptors is reduced by 10(2)-10(6)-fold. Light-induced bumps recorded from even the most severely affected mutants are physiologically normal. Moreover, a detailed noise analysis shows that photoreceptor responses of both a ninaE mutant and a ninaD mutant follow the adapting bump model. Since any extensive rhodopsin-rhodopsin interactions are not likely in these mutants, the above results suggest that such interactions are not needed for the generation and adaptation of light-induced bumps. Mutant bumps are strikingly larger in amplitude than wild-type bumps. This difference is observed both in ninaD and ninaE mutants, which suggests that it is due to severe depletion of rhodopsin content, rather than to any specific alterations in the opsin protein. Lowering or buffering the intracellular calcium concentration by EGTA injection mimics the effects of the mutations on the bump amplitude, but, unlike the mutations, it also affects the latency and kinetics of light responses.

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Changes in Intracellular Calcium Concentration Affect Desensitization of GABAA Receptors in Acutely Dissociated P2–P6 Rat Hippocampal Neurons

Journal of Neurophysiology ◽

10.1152/jn.1998.79.3.1321 ◽

1998 ◽

Vol 79 (3) ◽

pp. 1321-1328 ◽

Cited By ~ 14

Author(s):

Jerzy W. Mozrzymas ◽

Enrico Cherubini

Keyword(s):

Intracellular Calcium ◽

Hippocampal Neurons ◽

Calcium Concentration ◽

Intracellular Calcium Concentration ◽

Potential Range ◽

Patch Clamp Technique ◽

Whole Cell ◽

Cell Configuration ◽

High Calcium ◽

Kinetics Of

Mozrzymas, Jerzy W. and Enrico Cherubini. Changes in intracellular calcium concentration affect desensitization of GABAA receptors in acutely dissociated P2–P6 rat hippocampal neurons. J. Neurophysiol. 79: 1321–1328, 1998. The whole cell configuration of the patch-clamp technique was used to study the effects of different cytosolic calcium concentrations [Ca2+]i on desensitization kinetics of γ-aminobutyric acid (GABA)-activated receptors in acutely dissociated rat hippocampal neurons. Two different intrapipette concentrations of the calcium chelator 1,2-bis(2-aminophenoxy)ethane- N, N, N′, N′-tetraacetic acid (BAPTA; 11 and 0.9 mM, respectively) were used to yield a low (1.2 × 10−8 M) or a high (2.2 × 10−6 M) [Ca2+]i. In low [Ca2+]i, peak values of GABA-evoked currents (20 μM) evoked at −30 mV, were significantly larger than those recorded in high calcium [2,970 ± 280 (SE) pA vs. 1,870 ± 150 pA]. The extent of desensitization, assessed from steady-state to peak ratio was significantly higher in high calcium conditions (0.14 ± 0.007 vs. 0.11 ± 0.008). Similar effects of [Ca2+]i on desensitization were observed with GABA (100 μM). Recovery from desensitization, measured at 30 s interval with double pulse protocol was significantly slower in high [Ca2+]i than in low [Ca2+]i (54 ± 3% vs. 68 ± 2%). The current-voltage relationship of GABA-evoked currents was linear in the potential range between −50 and 50 mV. The kinetics of desensitization process including the rate of onset, extent of desensitization, and recovery were voltage independent. The run down of GABA-evoked currents was faster with the higher intracellular calcium concentration. The run down process was accompanied by changes in desensitization kinetics: in both high and low [Ca2+]i desensitization rate was progressively increasing with time as the slow component of the desensitization onset was converted into the fast one. In excised patches, the desensitization kinetics was much faster and more profound than in the whole cell configuration, indicating the involvement of intracellular factors in regulation of this process. In conclusion, [Ca2+]i affects the desensitization of GABAA receptors possibly by activating calcium-dependent enzymes that regulate their phosphorylation state. This may lead to modifications in cell excitability because of changes in GABA-mediated synaptic currents.

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