RESUMO
cGMP markedly increases the cationic conductance of the 'inside-out' patches of rod outer segment plasma membrane when applied to the inner side. The cGMP-activated conductance of some patches was shown to be time-dependent. The data obtained suggest that the change of cGMP concentration in the near membrane layer underlies this phenomenon rather than the change in the channel's activity. The hydrolysis and, probably, the desorption of the nucleotide are responsible for this.
Assuntos
GMP Cíclico/farmacologia , Peptídeos e Proteínas de Sinalização Intracelular , Células Fotorreceptoras/fisiologia , Segmento Externo da Célula Bastonete/fisiologia , Animais , Proteínas de Transporte/fisiologia , Membrana Celular/efeitos dos fármacos , Membrana Celular/fisiologia , Condutividade Elétrica , Modelos Biológicos , Rana temporaria , Segmento Externo da Célula Bastonete/efeitos dos fármacosRESUMO
Using a 'patch-clamp' method in the 'inside-out' configuration, ATP, ADP, AMP-PCP and AMP-PNP have been shown to increase the cGMP-dependent component of the rod plasma membrane conductance 2-4-fold and GTP, GDP but not GMP or nonhydrolyzable GTP analogs GMP-PNP and GTP-gamma-S to abolish the ATP action. The ATP and GTP effects were observed at [EDTA] = 1 mM when magnesium and calcium ions were absent. In about half of the experiments the cGMP-dependent conductance was shown to be increased by cAMP in the micromolar concentration range by 10-50%, the cAMP action did not depend on the presence of nucleoside triphosphates. In vivo ATP, GTP and cAMP are assumed to modulate the sensitivity of the photoreceptor plasma membrane to cGMP.
Assuntos
Trifosfato de Adenosina/farmacologia , AMP Cíclico/farmacologia , GMP Cíclico/farmacologia , Guanosina Trifosfato/farmacologia , Células Fotorreceptoras/fisiologia , Nucleotídeos de Adenina/farmacologia , Animais , Membrana Celular/fisiologia , Interações Medicamentosas , Ácido Edético/farmacologia , Condutividade Elétrica , Nucleotídeos de Guanina/farmacologia , Células Fotorreceptoras/efeitos dos fármacos , Rana temporaria , Xenopus laevisRESUMO
Antiidiotypic approach was used to obtain antibodies interacting with cGMP-binding site of the cGMP-activated channel of the photoreceptor cell. Monoclonal anti-BrcGMP antibodies having characteristics of binding of agonist and its analogs close to those for a natural receptor have been obtained. These antibodies were used to raise polyclonal antiidiotypic antibodies capable of interacting with a natural cGMP-receptor. Application of immunoglobulins, isolated from antiidiotypic serum, to inside-out fragments of the rod plasma membrane led to an irreversible increase of the conductance of cGMP-dependent channels.