RESUMO
Several Na(+) transporters are functionally abnormal in the hypertensive rat. Here, we examined the effects of a high-salt load on renal Na(+),K(+)-ATPase and the sodium-coupled glucose transporter (SGLT1) in Dahl salt-resistant (DR) and salt-sensitive (DS) rats. The protein levels of Na(+),K(+)-ATPase and SGLT1 in the DS rat were the same as those in the DR rat, and were not affected by the high-salt load. In the DS rat, a high-salt load decreased Na(+),K(+)-ATPase activity, and this decrease coincided with a decrease in the apparent Mechaelis constant (K(m)) for ATP, but not with a change of maximum velocity (V(max)). On the contrary, a high-salt load increased SGLT1 activity in the DS rat, which coincided with an increase in the V(max) for alpha-methyl glucopyranoside. The protein level of phosphorylated tyrosine residues in Na(+),K(+)-ATPase was decreased by the high-salt load in the DS rat. The amount of phosphorylated serine was not affected by the high-salt load in DR rats, and could not be detected in DS rats. On the other hand, the amount of phosphorylated serine residues in SGLT1 was increased by the high-salt load. However, the phosphorylated tyrosine was the same for all samples. Therefore, we concluded that the high-salt load changes the protein kinase levels in DS rats, and that the regulation of Na(+),K(+)-ATPase and SGLT1 activity occurs via protein phosphorylation.
Assuntos
Hipertensão/metabolismo , Rim/metabolismo , Glicoproteínas de Membrana/metabolismo , Proteínas de Transporte de Monossacarídeos/metabolismo , ATPase Trocadora de Sódio-Potássio/metabolismo , Animais , Glucose/metabolismo , Immunoblotting , Cinética , Proteínas de Membrana/metabolismo , Fosforilação , Ratos , Ratos Endogâmicos Dahl , Sódio/metabolismo , Transportador 1 de Glucose-Sódio , ATPase Trocadora de Sódio-Potássio/genéticaRESUMO
A 22-year-old male who had been receiving insulin therapy to treat uncontrollable hyperglycemia, was diagnosed to have a carcinoid in the lower rectum. The excised tumor was 1.5 cm in diameter, and showed a yellowish-white cut surface. It did not invade into the proper muscle. Numerous glucagon immunoreactive cells were found. The tumor cells contained many rounded neurosecretory granules. After tumor excision, the patient's hyperglycemia did not return in the absence of insulin administration. We suggest that the tumor may have secreted glucagon which may have acted as an antagonist against insulin in the circulation.