RESUMEN
We investigated the effects of vitamins C and E on the delayed-rectifier potassium current (IK(DR)), which is important in repolarizing the membrane potential, and on the transient A-type potassium current (IK(A)), which regulates neuronal firing frequency. The whole-cell patch-clamp technique was used to measure the currents from cultured Drosophila neurons derived from embryonic neuroblasts. The membrane potential was stepped to different voltages between -40 and +60 mV from a holding potential of -80 mV. IK(DR) and IK(A) measured in the vitamin C-containing solution (IK(DR) 305 +/- 16 pA, IK(A) 11 +/- 2 pA) were smaller than those measured in the control solution (488 +/- 21 pA, IK(A )28 +/- 3 pA). By contrast, IK(DR) and IK(A) measured in the vitamin E-containing solution (IK(DR) 561 +/- 21 pA, IK(A )31 +/- 3 pA) were greater than those measured in the control solution (422 +/- 15 pA, 17 +/- 2 pA). These results indicate that vitamins C and E can modulate potassium current amplitudes and possibly lead to altered neuronal excitability.
Asunto(s)
Antioxidantes/farmacología , Ácido Ascórbico/farmacología , Neuronas/efectos de los fármacos , Canales de Potasio de Rectificación Interna/metabolismo , Vitamina E/farmacología , Animales , Células Cultivadas , Drosophila melanogaster/efectos de los fármacos , Drosophila melanogaster/embriología , Drosophila melanogaster/metabolismo , Embrión no Mamífero/efectos de los fármacos , Femenino , Potenciales de la Membrana/efectos de los fármacos , Potenciales de la Membrana/efectos de la radiación , Neuronas/metabolismo , Técnicas de Placa-Clamp/métodos , Potasio/metabolismoRESUMEN
We investigated the effects of caffeine on the delayed-rectifier potassium current (IK(DR)) which is important in repolarizing the membrane potential, and the transient A-type potassium current (IK(A)) which regulates neuronal firing threshold and the rate of repetitive action potentials. The whole-cell patch-clamp technique was used to measure the currents from cultured Drosophila neurons derived from embryonic neuroblasts. The currents were measured from neurons before and after the application of 1mM caffeine to the external saline of the same neuron. IK(DR) measured in the caffeine-containing solution (470+/-36 pA, n=18), was smaller than that measured in the control 6K/0Ca Tris solution (745+/-51 pA, n=18). IK(A) measured in the caffeine-containing solution (17+/-2 pA, n=16) was smaller than that measured in the control 6K/0Ca Tris solution (35+/-4 pA, n=16). These results indicate that caffeine reduces IK(DR) and IK(A) amplitudes and possibly leads to increased action potential frequency and enhanced neuronal excitability.
Asunto(s)
Cafeína/farmacología , Estimulantes del Sistema Nervioso Central/farmacología , Neuronas/efectos de los fármacos , Canales de Potasio de Rectificación Interna/metabolismo , Animales , Células Cultivadas , Relación Dosis-Respuesta en la Radiación , Drosophila , Estimulación Eléctrica/métodos , Embrión no Mamífero , Potenciales de la Membrana/efectos de los fármacos , Potenciales de la Membrana/efectos de la radiación , Neuronas/metabolismo , Técnicas de Placa-Clamp/métodos , Potasio/farmacologíaRESUMEN
The potassium A-current (IK(A)) is important in regulating the membrane potential between action potentials. The whole-cell patch-clamp technique was applied to cultured Drosophila neurons derived from embryonic neuroblasts. IK(A) was measured from neurons before and after application of 0.1 mM lanthanum to the external saline. IK(A) was smaller in the lanthanum-containing saline (7+/-1 pA) than in the control saline (34+/-6 pA). Activation and inactivation of IK(A) were unchanged by lanthanum. These results suggest that lanthanum neurotoxicity may lead to increased neuronal excitability. Moreover, given this inhibition of IK(A), lanthanum should not be used to block calcium current in studies of K+ currents.
Asunto(s)
Drosophila melanogaster/embriología , Lantano/metabolismo , Neuronas/metabolismo , Bloqueadores de los Canales de Potasio/metabolismo , Canales de Potasio de Rectificación Interna/metabolismo , 4-Aminopiridina/metabolismo , Animales , Células Cultivadas , Potenciales de la Membrana/fisiología , Neuronas/citología , Técnicas de Placa-ClampRESUMEN
The delayed-rectifier potassium current (IKDR) is important in repolarizing the membrane potential and determining the level of neuronal excitability. We investigated the effect of cadmium on this potassium current. The whole-cell patch-clamp technique was used to measure IKDR from cultured Drosophila neurons derived from embryonic neuroblasts. The current was measured from neurons before and after the application of 0.1 mM cadmium to the external saline. IKDR was similar in the cadmium-containing saline (383 +/- 47 pA) and the control saline (401 +/- 60 pA). These results indicate that cadmium neurotoxicity does not specifically affect IKDR in Drosophila neurons.
Asunto(s)
Cadmio/farmacología , Neuronas/efectos de los fármacos , Canales de Potasio de Rectificación Interna/efectos de los fármacos , Animales , Células Cultivadas , Drosophila , Embrión no Mamífero , Potenciales de la Membrana/efectos de los fármacos , Neuronas/metabolismo , Técnicas de Placa-Clamp/métodos , Bloqueadores de los Canales de Potasio/farmacología , Canales de Potasio de Rectificación Interna/metabolismo , Tetraetilamonio/farmacologíaRESUMEN
Learning and memory are defective in the Drosophila mutant rutabaga, which has a low intracellular cyclic adenosine monophosphate (cAMP) concentration. The aim of this study was to compare modulation effects of protein kinase C activator (PKC-A) on the delayed-rectifier potassium current (IKDR) in wild-type and rutabaga neurons. IKDR was measured from cultured (2 days) wild-type and rutabaga neurons. The authors examined the effects of PKC-A on IKDR in wild-type and rutabaga neurons. IKDR was measured from neurons before and after addition of PKC-A to the external solution. IKDR was smaller in rutabaga neurons (380 +/- 25 pA) than in wild-type neurons (529 +/- 44 pA). IKDR was reduced by PKC-A more in wild-type (decreasing 55 +/- 6%) than in rutabaga (decreasing 35 +/- 8%) neurons (single-cell studies). In the presence of PKC-A, there was no difference in IKDR between wild-type (229 +/- 31 pA) and rutabaga (242 +/- 26 pA) neurons (population studies). These results indicate that PKC-A differentially affects the delayed-rectifier channel in wild-type rutabaga.
Asunto(s)
Proteínas de Drosophila/metabolismo , Activadores de Enzimas/farmacología , Neuronas/efectos de los fármacos , Canales de Potasio de Rectificación Interna/metabolismo , Proteína Quinasa C/metabolismo , Animales , Animales Modificados Genéticamente , Células Cultivadas , Drosophila , Conductividad Eléctrica , Electrofisiología , Embrión no Mamífero , Genotipo , Potenciales de la Membrana/efectos de los fármacos , Neuronas/fisiología , Técnicas de Placa-Clamp/métodos , Potasio/metabolismo , Canales de Potasio de Rectificación Interna/efectos de los fármacosRESUMEN
The delayed-rectifier potassium current (IKDR) is important in regulating neuronal excitability. The authors characterized the neurotoxic effect of lanthanum on IKDR. The conventional whole-cell patch-clamp technique was applied to cultured Drosophila neurons derived from embryonic neuroblasts. IKDR was measured from neurons before and after application of 0.1 mM lanthanum to the external saline. IKDR was smaller in the lanthanum-containing saline (441 +/- 57 pA) than in the control saline (680 +/- 35 pA) (p <.001). Activation and inactivation of IKDR were unchanged by lanthanum. Because these results suggest that lanthanum acts as a potent blocker of IKDR, neuronal excitability may be altered during lanthanum neurotoxicity.
Asunto(s)
Lantano/farmacología , Neuronas/efectos de los fármacos , Bloqueadores de los Canales de Potasio/farmacología , Canales de Potasio de Rectificación Interna/antagonistas & inhibidores , Animales , Bloqueadores de los Canales de Calcio/farmacología , Células Cultivadas , Drosophila , Embrión no Mamífero , Activación del Canal Iónico/efectos de los fármacos , Potenciales de la Membrana/efectos de los fármacos , Neuronas/metabolismo , Técnicas de Placa-Clamp/métodos , Tetraetilamonio/farmacologíaRESUMEN
The transient K+ current (IK(A)) affects the rate of repetitive action potentials. The whole-cell patch-clamp technique was applied to cultured Drosophila neurons derived from embryonic neuroblasts. IK(A) was measured from neurons before and after application of 0.1 mM copper to the external saline. IK(A) was smaller in the copper-containing saline (12.0 +/- 1.6 pA) than in the control saline (37 +/- 6.5 pA). Activation and inactivation of IK(A) were unchanged by copper. These results suggest that copper can influence neuronal excitability and may affect neuronal function.
Asunto(s)
Cobre/farmacología , Neuronas/efectos de los fármacos , Bloqueadores de los Canales de Potasio/farmacología , 4-Aminopiridina/farmacología , Animales , Drosophila , Neuronas/metabolismoRESUMEN
The Drosophila learning mutant rutabaga is defective in short-term memory and has a reduced intracellular cyclic adenosine monophosphate (cAMP) concentration. The delayed-rectifier potassium current (IKDR) was measured from cultured (2 days) wild-type and rutabaga neurons. IKDR was smaller in rutabaga neurons (382 +/- 41 pA) than in wild-type neurons (542 +/- 33 pA). IKDR was measured from neurons before and after addition of serotonin to the external solution. IKDR was reduced by serotonin in wild type (decreasing 37 +/- 7%) and rutabaga (decreasing 33 +/- 6%) neurons (single-cell studies). In the presence of serotonin, IKDR was smaller in rutabaga (218 +/- 24 pA) than in wild-type (426 +/- 35 pA) neurons (population studies). These results indicate that serotonin has affected IKDR so that the inherent difference between the two genotypes was preserved.
Asunto(s)
Trastornos de la Memoria/fisiopatología , Neuronas/efectos de los fármacos , Canales de Potasio/fisiología , Potasio/metabolismo , Serotonina/farmacología , Animales , Animales Modificados Genéticamente , Brassica napus , Tamaño de la Célula , Células Cultivadas , Drosophila , Potenciales de la Membrana/efectos de los fármacos , Trastornos de la Memoria/genética , Mutación , Conducción Nerviosa/efectos de los fármacos , Neuronas/fisiología , Técnicas de Placa-Clamp , Canales de Potasio/efectos de los fármacosRESUMEN
In the Drosophila mutant rutabaga, short-term memory is deficient and intracellular cyclic adenosine monophosphate (cAMP) concentration is reduced. We characterized the delayed-rectifier potassium current (IK(DR)) in rutabaga as compared with the wild-type. The conventional whole-cell patch-clamp technique was applied to cultured Drosophila neurons derived from embryonic neuroblasts. IK(DR) was smaller in rutabaga (368 +/- 11 pA) than in wild-type (541 +/- 14 pA) neurons, measured in a Ca(2+)-free solution. IK(DR) was clearly activated at approximately 0 mV in the two genotypes. IK(DR) typically reached its peak within 10-20 msec after the start of the pulse (60 mV). There was no difference in inactivation of IK(DR) for wild-type (14 +/- 3%) and rutabaga (19 +/- 3%). After application of 10 mM TEA, in wild-type, IK(DR) was reduced by 46 +/- 5%, whereas in rutabaga, IK(DR) was reduced by 28 +/- 3%. Our results suggest that IK(DR) is carried by two different types of channels, one which is TEA-sensitive, whereas the other is TEA-insensitive. Apparently, the TEA-sensitive channel is less expressed in rutabaga neurons than in wild-type neurons. Conceivably, altered neuronal excitability in the rutabaga mutant could disrupt the processing of neural signals necessary for learning and memory.