RESUMO
Loss of venom from the venom gland after biting or manual extraction leads to morphological changes in venom secreting cells and the start of a cycle of production of new venom. We have previously shown that stimulation of both alpha- and beta-adrenoceptors in the secretory cells of the venom gland is essential for the onset of the venom production cycle in Bothrops jararaca. We investigated the signaling pathway by which the alpha-adrenoceptor initiates the venom production cycle. Our results show that the alpha(1)-adrenoceptor subtype is present in venom gland of the snake. In quiescent cells, stimulation of alpha(1)-adrenoceptor with phenylephrine increased the total inositol phosphate concentration, and this effect was blocked by the phospholipase C inhibitor U73122. Phenylephrine mobilized Ca(2+) from thapsigargin-sensitive stores and increased protein kinase C activity. In addition, alpha(1)-adrenoceptor stimulation increased the activity of ERK 1/2, partially via protein kinase C. Using RT-PCR approach we obtained a partial sequence of a snake alpha(1)-adrenoceptor (260 bp) with higher identity with alpha(1D) and alpha(1B)-adrenoceptors from different species. These results suggest that alpha(1)-adrenoceptors in the venom secreting cells are probably coupled to a G(q) protein and trigger the venom production cycle by activating the phosphatidylinositol 4,5-bisphosphate and ERK signaling pathway.
Assuntos
MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Fosfatidilinositol 4,5-Difosfato/química , Receptores Adrenérgicos alfa 1/fisiologia , Animais , Bothrops , Cálcio/metabolismo , Inibidores Enzimáticos/farmacologia , Estrenos/farmacologia , Feminino , Sistema de Sinalização das MAP Quinases , Masculino , Proteína Quinase C/metabolismo , Pirrolidinonas/farmacologia , Receptores Adrenérgicos alfa 1/metabolismo , Transdução de Sinais , Venenos de Serpentes , Tapsigargina/farmacologiaRESUMO
The noradrenergic innervation of Bothrops jararaca venom gland is thought to be important in the production and secretion of venom. We investigated the characteristics of the alpha-adrenoceptor in the venom gland and its role in venom production. This receptor had relatively low sensitivity to noradrenaline (pD(2)=4.77+/-0.09, N=7) and to phenylephrine (pD(2)=3.77+/-0.06, N=11). The receptor became desensitized just after venom extraction (pD(2) to phenylephrine fell to 3.27+/-0.02, N=6) and the sensitivity remained low for at least 15 days, returning to normal 30 days after venom extraction, by which time the snake was ready for a new cycle of venom production. Incubation of secretory cells with noradrenaline (10(-4) mol l(-1) for 5 min) reduced alpha-adrenoceptor sensitivity to the level seen after venom extraction. Blockade of catecholamine production with reserpine abolished the enlargement of the rough endoplasmic reticulum and the activation of the Golgi apparatus that are normally seen after venom extraction, and the venom production was restored by a single subcutaneous (s.c.) injection of phenylephrine (100 mg kg(-1)) immediately after venom extraction. Our data suggest that stimulation of the alpha-adrenoceptor during or shortly after biting is essential for the onset of the venom production cycle.
Assuntos
Bothrops/fisiologia , Venenos de Crotalídeos/biossíntese , Venenos de Crotalídeos/metabolismo , Glândulas Exócrinas/fisiologia , Receptores Adrenérgicos alfa/metabolismo , Animais , Catecolaminas/antagonistas & inibidores , Relação Dose-Resposta a Droga , Glândulas Exócrinas/metabolismo , Técnicas Histológicas , Norepinefrina/metabolismo , Fenilefrina/metabolismo , Reserpina/farmacologiaRESUMO
The noradrenergic innervation of Bothrops jararaca venom gland is thought to be important in the production and secretion of venom. We investigated the characteristics of the alpha-adrenoceptor in the venom gland and its role in venom production. This receptor had relatively low sensitivity to noradrenaline (pD(2)=4.77+/-0.09, N=7) and to phenylephrine (pD(2)=3.77+/-0.06, N=11). The receptor became desensitized just after venom extraction (pD(2) to phenylephrine fell to 3.27+/-0.02, N=6) and the sensitivity remained low for at least 15 days, returning to normal 30 days after venom extraction, by which time the snake was ready for a new cycle of venom production. Incubation of secretory cells with noradrenaline (10(-4) mol l(-1) for 5 min) reduced alpha-adrenoceptor sensitivity to the level seen after venom extraction. Blockade of catecholamine production with reserpine abolished the enlargement of the rough endoplasmic reticulum and the activation of the Golgi apparatus that are normally seen after venom extraction, and the venom production was restored by a single subcutaneous (s.c.) injection of phenylephrine (100 mg kg(-1)) immediately after venom extraction. Our data suggest that stimulation of the alpha-adrenoceptor during or shortly after biting is essential for the onset of the venom production cycle.