Roles of Na⁢-Ca2⁢ Exchange in the Negative Force-Frequency Relationship

• 영문명: Roles of Na^⁢-Ca^2⁢ Exchange in the Negative Force-Frequency Relationship
• 발행기관: 대한생리학회-대한약리학회
• 저자명: Chang Mann Ko Soon Jin Kim
• 간행물 정보: 『The Korean Journal of Physiology & Pharmacology』제2권 제6호, 715~724쪽, 전체 10쪽
• 주제분류: 의약학 > 의학일반
• 파일형태: PDF
• 발행일자: 1998.01.01

영문 초록

Frequency-force relationships (FFR) were studied in electrically field stimulated rat left atria (LA) by reducing the stimulation frequency from resting 3 Hz to test frequencies (0.1-1 Hz) for 5 minutes. The twitch amplitudes of LA elicited the typical negative staircases with 3-phased changes: the initial rapid increase, the second decrease and the following plateau at test frequencies. Verapamil (3⁓10^⁣5 M) pretreatment elicited frequency-dependent suppression of the twitch amplitudes, exaggerating the negative staircase. Monensin pretreatment enhanced not the peak but the plateau amplitudes in a concentration-dependent manner. When the Na^⁢-Ca^2⁢ exchange was blocked by Na^⁢ and Ca^2⁢ depletion in the Krebs Hensleit buffer (0 Na^⁢-0 Ca^2⁢ KHB), the twitch amplitudes increased in a frequency-dependent manner, changing the negtive staircase into the positve one. Meanwhile, the 0 Na^⁢-0 Ca^2⁢ KHB applicationinduced enhancement was strongly suppressed by caffeine (5 mM) pretreatment. Only dibucaine among the local anesthetics increased the basal tone during frequency reduciton. There were no differences in ⁴⁵Ca uptakes between 0.3 Hz and 3 Hz stimulation except at 1 min when it was significantly low at 0.3 Hz than 3 Hz, illustrating net Ca^2⁢ losses. Monensin pretreatment enhanced the rate of this Ca^2⁢ loss. Taken together, it is concluded that Na^⁢-Ca^2⁢ exchange extrudes more SR released Ca^2⁢ out of the cell in proportion to the frequency, resulting in the negative rate staircase in the rat LA.

키워드

Negative staircase Na^⁢ -Ca^2⁢ exchange Ca^2⁢ extrusion Dibucaine