ABSTRACT
BACKGORUND: Capacitive calcium entry involves the influx of Ca2+ across the sarcolemma in response to the depletion of intracellular Ca2+ stores. Presently, little is known about the nature of the intracellular Ca2+ store (s) in pulmonary arterial smooth muscle cells (PASMCs), even though the unique contractile response of this tissue to hypoxia may at least partially involve the intracellular release of Ca2+ . The authors aimed to investigate the effects of nicardipine on capacitative calcium entry. METHODS: isolated pulmonary smooth muscle cells were obtained from enzymatically treated canine pulmonary artery. Currents were recorded at room temperature using the dialyzed whole cell recording technique. The protocol used to deplete intracellular Ca2+ stores and to monitor the development of the store-operated Ca2+ currents, involved cells being were voltage-clamped at 0 mv to inactivate any voltage-dependent calcium currents, which were recorded in response to a 200 ms voltage step from 120 to 40 mV in 20 mV increments. RESULTS: Simultaneous depletion of intracellular Ca2+ leads to linear store-operated Ca2+ current (iSOC) reversal near 0 mV. Nicardipine does not affect iSOC. CONCLUSiONS: in canine PASMCs, the depletion of intracellular Ca2+ stores leads to the activation of iSOC, which is not inhibited by nicardipine, a voltage-dependent Ca2+ channel (VDCC) blocker, indicating that VDCC blocked by nicardipine does not contribute to CCE in canine PASMCs.
Subject(s)
Hypoxia , Calcium Channels , Calcium , Muscle, Smooth , Myocytes, Smooth Muscle , Nicardipine , Patch-Clamp Techniques , Pulmonary Artery , SarcolemmaABSTRACT
BACKGROUND: Morphine has a direct action on morphine receptors in the brain and spinal cord. Intrathecally administered L-NAME, a nitric oxide synthase inhibitor, is known to have an antinociceptive effect on formalin-induced pain in animal studies. Efficacy of intrathecally administered ketorolac, a cyclooxygenase inhibitor, is somewhat controversial. The interactions of intrathecally administered morphine, ketorolac and L-NAME on formalin-induced nociception was studied. METHODS: Male Sprague-Dawley rats were implanted with chronic lumbar intrathecal catheters and were tested for paw flinch by a formalin injection. Drugs were intrathecally administered 15 min before the formalin injection, and biphasic painful behaviors were observed. We obtained the ED50 for each agent (ketorolac, L-NAME and morphine). ED50 fractions (1, 1/2 and 1/4) of drug combinations of L-NAME-ketorolac, morphine-L-NAME and ketorolac-morphine were administered. The ED50 of each combined drug was established and isobolographic analysis of the drug interactions was carried out. RESULTS: Intrathecal administration of ketorolac, L-NAME and morphine produced a dose-dependent suppression of pain behaviors in phase 2. ED50 values were 297.04micro gram for ketorolac, 207.46micro gram for L-NAME and 0.17micro gram for morphine in phase 2. Isobolographic analysis showed that the combination of intrathecal morphine and L-NAME synergistically reduced pain behaviors in phase 2. CONCLUSIONS: Intrathecally administered morphine, L-NAME and ketorolac produced a dose-dependent decrease in the number of paw flinches in both phase 1 and phase 2 on the formalin test. Morphine with L-NAME showed synergistic analgesic effects on formalin-induced pain in phase 2.