Measurement of Ca2+ sensitivity in rat ventricular muscles in isotonic contraction

4. Oral Presentations O-18

A21

measurement of Ca”’ sensitivity muscles in isotonic contraction Tetsuya Ishikawa The Jikei University

School of Medicine, whether

be

Juichiro Shimizu, Daniel Burkhoff, Gentaro Iribe. Satoshi Mohri, Junichi Araki & Fumihiko Kajiya. Dept of Cardiovascular Physioi., Okayama Univ. Grad. Sch. of Med & Dent., Okayama, Japan : The force-calcium relationship can characterize I e properties of ventricular. myocard~~m. However, this analysis requires a skinned muscle preparation or tetanization with calcium measurement. Using 4-state biochemical interaction model, we succeeded in mimicking skinned muscle preparations and in comparing the force-calcium relations in physiologically contracting preparations. The purpose of this study was to compare the forcecalcium relationship between isolated, blood-perfused canine hearts 13%37°C) and crystalloid superfused ferret papillary muscles (30°C). methods: We used six isolated cross-circulated, blood-perfused canine hearts. We recorded isovolumic left ventricular (LV) pressure and measured calcium transient by macro-injected aequorin. We also used six ferret papillary muscles perfused with Tyrode solution and recorded isometric tension and aequorin signal. We obtained these data at different i’v’ volumes and muscle lengths. We determined length-dependent rate constants of the 4-state model so that the predicted stress or tension curves best fit the measured curves. Constant calcium signals input to the @state model instead of observed calcium transtents well mimicked the response of We compared K50 as an index of skinned muscle preparations. cium sensitivity and Hill coefficient as an index of cooperativity. suits: Canine hearts had K50 significantly smaller than ferret papillary muscles (0.056cO.02’l~M vs. 0.349iC.O82~M, at maximal However, there was no significrlnt strain and length, p
estimated

pCa-shortening dissected

The aequorin (iCa”]i)

sinlult~eousiy induced fixed

at the resting

was obtained

level

using

(duration

(@a.~, ,,IOI,,~U,c,and pC&

~soiiicurc~ (6.02

i

sensitivity

of rat ventricular contraction

tension

10

was

The relations

[Ca”]o

which ([Ca”]o)

were &ted

in each contraction

was

gave the 50% of maximal

(saton,cj). The mean value of pCaSu

1.12) was not significantly (n=6,

was

col~ce~~a~on

under various

Ca*+ sensitivity of pCa which

Tetanlls

to the maximum

of 20 n&l Ca”

Ca2’ were

40 ms, frequency

system.

relative

(,ioron,sj (6.061

0.52)

muscles

tensiovl

In shortening,

a feedback

measured

equation.

as the value

contraction

the stimulation.

of contraction

in the solution

the Hill

estimated

6 s after stimulation

and pCa (=-log@‘]i) with

or developed

of 5 /.I M ryanodine.

between the magnitude

compared

in the same

of the rat, and the intracellular

and slmrtening

by a repetitive

we

relation

method was apphed to papillary

measured

Hz) in the presence

of the nlyo~Iarnellts

contractions,

pCa+ension

from the right ventricle

concentration

Tokyo, Japan, 105-8461

isotonic with

*

(II ) ‘,

the Ca”sensitivity

during

relation

preparations.

isotonic

N OF CALCIUM-S~N§l~iVlTY CAL PREPARATIONS OF ~A~1

‘, Satoshi Kurihara

’ and Physiology

In order to examine can

Ca”+ waves have been implicated in some types of cardiac arrh~hrn~a~ however: their prope~ies were mostly st~die(~ in isolated single cells but not in m~lt~ceilular preparat~o~!~. In this study, we examined possibility of intercel~~iar propagation of Ca*+ waves and regulation of their occurrence in intact guinea pig ventricular muscle. papillar muscles were loaded with flue-3 or rhod-2 and surface cells of the preparation were confocal microscope. No Ca2+ waves der resting condition. Frequent Ca” waves were observes at a stimulation rate of treater than 2 Hz. We examined effects of several alerts including $timuiatio~ frequency, extrace~iular [Ca’+], [Na’], and [K’], and cycio~ia~onic acid on the waves, paying attention to their amplitude, duration, propagation velocity and occurra~ce interval. Our results s~~~e~t that Ca”” loadirlg level of sarcoplasmic reticulum may be the most impo~ant factor for induction of Ca” waves. Those Ca2+ haves, however, seldom propa ated before cell boundary.

I, Seibu Mochizuki

of Cardioloa

Department

in rat ve~tricuiar

different

mean t muscles

SD).

that of pCaSo

from

Therefore,

the

can also be estimated

using pca~s~o~e~~ng

Ca’* during

relation.

O-20

Junishl ~AJIYA,

Abel,

Juichiro

Department

§H~~l~U, of Cardiovascular

university Graduate School of Okayam~~

Satoshi ~~~R~, Physiology,

~umihik~ ~kayama

edicine and dentists,

Japan

a~~~ro~n~: Left ventricular (LV) pe~or~~~ reflects transmural nano-order dynamics of actin-myosin interactions of the heart Ultrabrilliant x-ray provided by Spring-8 (8 GeV), the world largest synchrotron radidion facility is the rest powerful tool for direct, in vivc, real-time evaluation of cardiac nano-mechanics.

torpor:

To analyze

real-llrns

transmural

crossbridge

dynamics

of a

beating rat LV, we utilized Spring-8 x-ray equatonai diffra~ion pattern from the actin-nyosin lattice structure of myocardium. Methods: lsovolumicaily beating rat hearts (n=8j artdicially paced were mounted on a turning stage so that the direction of incoming xray was sagtttaito the hearts. While x-ray scanned the LV free wall tangentially from epicardium to e~docardium, 1, 0 and 1, 1 patterns of x-ray diffraction which reflect adiin-myosin ~ntera~ions, were drgitally recorded to a computer with the LV pressure and volutre data. Then, the hearts were fixed and sliced for comparison between x-ray observation and microscopic observation. Results: The x-ray diffra~ion pattern showed two concentric (I, 0 and 1, 1) circles having two high intensity axes. These high intensity axes turned in the opposite diredian with transmural x-ray scanning and had identical relations with microscopic structures of anterior or posterior wall. The (I, 1) / (I, 0) plane brightness intensity ratio was relevant to LV pressure deveiop~nt with a certain time delay. ~onciusion: The x-ray diffraction study with Spring-8 provides a powerful tool to analyze real-time, transmural nano-order crossbridge dynamics