RESUMO
The influence of electromagnetic fields (EMFs) with rectangular pulse frequencies of 8 and 50 Hz and flux density of 25 µT on contraction, nitric oxide/nitrite synthesis, and intracellular calcium concentration in the gastric smooth muscles of rats was investigated. An approximately 8-Hz field reduced the fast component of contraction induced by KCl depolarization and slowed down the time to reach the maximum of the slow component of contraction, whereas the 50-Hz field increased the fast and slow components and accelerated the time to reach the maximum of the slow component of contraction. After turning off the EMF, the force and character of contraction returned to the control values. In addition, the 8-Hz field increased nitric oxide/nitrite synthesis in the excited smooth muscle tissue with KCl depolarization, while the 50-Hz field had no significant effect. 8- and 50-Hz fields had no significant effects on nitric oxide/nitrite production in non-stimulated tissue. However, the 50-Hz field significantly increased the basic intracellular calcium concentration in smooth muscle cells (SMC) in a time-dependent manner, whereas the 8-Hz field only slightly increased calcium levels. Thus, we showed that responses of gastric smooth muscles to EMFs are pulse-frequency dependent.