Unfortunately, the phenomenon of myoplasmic Ca2+ oscillations
has thus far not been reported for intact smooth muscle tissue
from human blood vessels (although the first report of
intracellular Ca2+ waves was based on measurements done in
smooth muscle cells cultured from humans [11]). In a recent publication,
we documented this functional difference between vascular
smooth muscles of human and murine origin, while
demonstrating a striking difference in the membranous ultrastructure
of the smooth muscle derived from the two different sources
[12]. The human smooth muscle, which lacked Ca2+ oscillations,
had very little peripheral SR and practically no PM-SR junctions,
while the mice in accordance with previous reports responded to
adrenergic activation with asynchronous repetitive Ca2+ waves
and exhibited abundant peripheral SR and numerous PM-SR junctions.
In addition, we noted that while the human blood vessels
lacked Ca2+ oscillations the Rho-kinase component of their myofilament
activation was enhanced [12]. Since the human patients
supplying the blood vessels were generally elderly and of compromised
health, we hypothesized that in human vascular smooth
muscle the degradation of membranous ultrastructure leading to
loss of Ca2+ wave-like oscillations could be causally linked to the
development of vascular dysfunction and disease. Considering
the prevalence of human vascular disease and the amount of suffering it inflicts, it is clear that the above putative link between
aberrant Ca2+ signaling and vascular disease should be further
investigated. However, without clear evidence of Ca2+ oscillations
or waves in human vascular smooth muscle it could be argued that
human blood vessels are different from those of experimental
animals.
In this communication, we show for the first time that adrenergic
stimulation of human mesenteric arteries induces Ca2+ oscillations
in the medial smooth muscle cells. Since the challenges
facing online living human blood vessel research are considerably
greater than encountered in the laboratory animal, most of the
mechanistic details are usually first established in the latter. The
present demonstration that vascular Ca2+ signaling in humans involves
repetitive Ca2+ oscillations provides the clinical relevance
for their study in health and disease.